This invention relates to shell boilers, that is to say to a boiler having a shell containing water or a fluid, such as thermal fluid, to be heated; such a shell boiler normally has a furnace section in the form of a horizontal cylindrical tunnel extending through the boiler and in which combustion takes place. It is also usual to provide flue tubes extending horizontally through the water or fluid and to which the products of combustion are directed and which serve to heat the water further. The boiler may be used, for example, for generating steam or heating water or thermal fluid (oil).
British Patent Specification No. 1,426,579 shows a shell boiler containing water or other fluid to be heated with a removable furnace section providing a fluidised bed. Water or other fluid passes through tubing in the fluidised bed but is separate from the working fluid circuit.
It is an object of this invention to provide an improved shell boiler.